“…Batista et al (2012b) and Batista, Silvestre, and Oliveira (2012c) also considered the use of a separate observer to produce globally exponentially stable gyro bias estimates, although their approach requires stationary reference vectors. Attitude estimation using a single vector measurement has been considered by several authors (Batista et al, 2011b;Batista, Silvestre, & Oliveira, 2012a;Kinsey & Whitcomb, 2007;Lee, Leok, McClamroch, & Sanyal, 2007;Mahony, Hamel, Trumpf, & Lageman, 2009) and is possible under a persistency-of-excitation (pe) condition.…”